One goal of this program is to prepare irreversible inhibitors of the cAMP-specific and of the calmodulin-sensitive forms of cyclic nucleotide phosphodiesterase. Affinity probes will be used to determine part of the amino acid composition of the hydrolytic site of the calmodulin-sensitive phosphodiesterase. The relationship between irreversible inhibition in intact porcine coronary arteries and the intracellular levels of cyclic AMP and cyclic GMP will be determined in order to establish which form of the enzyme is mainly responsible for the regulation of each nucleotide. In a second aspect of this program, we will attempt to photoaffinity label and biochemically characterize the A2-Adenosine receptor. We have developed potent and relatively selective inhibitors of the two subtypes of adenosine receptor and, based on the structure activity relationships of these inhibitors, we will also design and prepare high affinity ligands to use in characterization of the A1 and the A2-adenosine receptors.